Multi-Antenna System, and Transmitting Apparatus and Method Based on Index Coding and Beamforming Thereof

1. An operating method of a transmitter having a plurality of antennas, the method comprising: classifying a plurality of receivers into at least one group; determining an index code for the group; designing a beamforming matrix for the group; and transmitting at least one of a plurality of files to the group through the antennas based on the index code and the beamforming matrix, wherein the designing of the beamforming matrix comprises: designing a first beamforming matrix for the group in order to prevent interference with the group; designing a second beamforming matrix for each receiver within the group; designing an initial beamforming matrix based on the first beamforming matrix and the second beamforming matrix; and designing the beamforming matrix based on a conjugate-gradient scheme using the initial beamforming matrix.

2. The method of claim 1 , wherein the conjugate-gradient scheme comprises a scheme for updating a solution by calculating a gradient when an objective function is differentiable, but the solution of a closed form is not found.

3. The method of claim 1 , wherein the designing of the beamforming matrix based on the conjugate-gradient scheme comprises: calculating a Riemannian gradient of an objective function by projecting the objective function based on the initial beamforming matrix onto a tangent space of a manifold indicative of a power condition for a DT-RCG algorithm.

4. The method of claim 1 , wherein the classifying of the plurality of receivers comprises: classifying the receivers based on information previously stored in relation to the receivers, wherein at least one of the receivers previously stores at least one of the files, and wherein the information comprises at least one of an identifier of the stored file or a channel value for each of the receivers with respect to each of the receivers.

5. A transmitter, comprising: a plurality of antennas; a processor connected to the antennas and configured to communicate with a plurality of receivers through the antennas; and a memory connected to the processor to store a plurality of files, wherein the processor is configured to: classify a plurality of receivers into at least one group, determine an index code for the group, design a beamforming matrix for the group, and transmit at least one of a plurality of files to the group through the antennas based on the index code and the beamforming matrix, wherein the processor is configured to: design a first beamforming matrix for the group in order to prevent interference with the group, design a second beamforming matrix for each receiver within the group, design an initial beamforming matrix based on the first beamforming matrix and the second beamforming matrix, and design the beamforming matrix based on a conjugate-gradient scheme using the initial beamforming matrix.

6. The transmitter of claim 5 , wherein the conjugate-gradient scheme comprises a scheme for updating a solution by calculating a gradient when an objective function is differentiable, but the solution of a closed form is not found.

7. The transmitter of claim 5 , wherein the processor is configured to calculate a Riemannian gradient of an objective function by projecting the objective function based on the initial beamforming matrix onto a tangent space of a manifold indicative of a power condition for a DT-RCG algorithm.

8. The transmitter of claim 5 , wherein the memory further stores information related to the receivers, and wherein the processor is configured to classify the receivers based on the information, wherein at least one of the receivers previously stores at least one of the files, and wherein the information comprises at least one of an identifier of the stored file or a channel value for each of the receivers with respect to each of the receivers.

9. A multi-antenna system, comprising: a plurality of receivers, each receiver comprising a plurality of antennas; and a transmitter configured to communicate with the receivers through the plurality of antennas, wherein the transmitter is configured to: classify a plurality of receivers into at least one group; determine an index code for the group; design a beamforming matrix for the group; and transmit at least one of a plurality of files to the group based on the index code and the beamforming matrix, wherein the transmitter is further configured to: design a first beamforming matrix for the group in order to prevent interference with the group; design a second beamforming matrix for each receiver within the group; design an initial beamforming matrix based on the first beamforming matrix and the second beamforming matrix; and design the beamforming matrix based on a conjugate-gradient scheme using the initial beamforming matrix.

10. The multi-antenna system of claim 9 , wherein the conjugate-gradient scheme comprises a scheme for updating a solution by calculating a gradient when an objective function is differentiable, but the solution of a closed form is not found.

11. The multi-antenna system of claim 9 , wherein the transmitter is configured to calculate a Riemannian gradient of an objective function by projecting the objective function based on the initial beamforming matrix onto a tangent space of a manifold indicative of a power condition for a DT-RCG algorithm.